U.S. Pat. No. 3,786,312 discloses a portable box for power distribution. Each of two circuits includes three outlets coupled to a ground fault interrupter.
U.S. Pat. No. 2,995,670 discloses a portable box supported on legs and providing power distribution suitable for television or motion picture studios. Busses of incoming and outgoing power cables allow connection of plural boxes in series. A series of outlets are coupled electrically to the busses of each box through circuit breakers. Cable strain relief clamps are provided.